Sorbent for binding metals and production thereof

ABSTRACT

The present invention relates to a sorbent which is suitable for binding metals from solutions, the production of a corresponding sorbent as well as the use of the sorbent for binding metals from solutions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing of International Appln.No. PCT/EP2015/001754, filed 28 Aug. 2015, and claims priority of GermanApplication No. 10 2014 012 566.1, filed 29 Aug. 2014, the entirety ofwhich applications are incorporated herein by reference for allpurposes.

The present invention relates to a sorbent which is suitable for bindingmetals from solutions, the production of a corresponding sorbent as wellas the use of the sorbent for binding metals from solutions.

The removal or extraction or recovery of metals, in particular heavymetals, from industrial waste waters, for example at plating plants,from catalyst residues from the petrochemical or pharmaceuticalindustry, from pit water for example from mines, the renaturation ofheavy metal-polluted soils etc. is an increasingly important problemsince heavy metals in particular either have a harmful effect on theenvironment and also their recovery is of economic interest. In otherwords, on the one hand environmental aspects are the priority, and onthe other, the provision of valuable metals, the availability of whichis becoming increasingly doubtful or the price of which is rising isalso of great interest. A further important field of use of sorbents forthe removal or extraction or recovery of metals or heavy metals is theremoval of these in drinking water purification and also in seawaterdesalination. Likewise, the removal of heavy metals from concentratedsalt solutions, such as are used in chloralkali electrolysis or similarprocesses, is also of great interest.

For the said areas of use, previously known phases/sorbents often do nothave adequate binding capacity for binding the metals to be bound on asufficient scale for example from high concentration or lowconcentration solutions or strongly acidic solutions, in particular alsoin the presence of alkali or alkaline earth metal ions. Furthermore,previously known phases often do not exhibit stability over the wholerange from pH 0 to pH 14. A further disadvantage of many previouslyknown phases is that the desired metal can indeed be bound, but cannotbe recovered simply or indeed at all from the sorbent used. Owing to themostly unsatisfactory binding capacity of known sorbents/phases, a highsorbent/phase volume is often required, as a result of which the metalbinding processes are very elaborate and cost-inefficient. Further,owing to the mostly low binding capacity of known metal-bindingsorbents, repeated operation of the process is necessary in order forexample to be able to provide heavy metal-free water as drinking water.

It was therefore the object of the present invention to provide a novelsorbent which partly or wholly does not exhibit the aforesaiddisadvantages. In particular, it is an object of the present inventionto provide a sorbent with a high binding capacity towards metals, inparticular heavy metals and noble metals, per gram or per millilitre.Preferably, the sorbent provided according to the invention is inparticular renewable with sodium hydroxide, or allows the recovery ofthe metals in a simple manner. A further object of the present inventionis to provide a sorbent which still has a relatively high bindingcapacity towards metals even under acidic conditions.

Furthermore, compared to the metal binding-sorbents known from the stateof the art, the volume of the sorbent used for the metal binding shouldbe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2: FIGS. 1 and 2 show the comparison of the isotherms of thesorbents from Example 1 and comparison example 1 in the binding ofcopper from aqueous solutions according to Example 2.

FIG. 3: FIG. 3 shows the metal binding capacity of the sorbent fromExample 1 for the metals copper, nickel and chromium as a function ofthe metal concentration according to Example 3.

FIG. 4: FIG. 4 shows the quantity of absorbed copper [g] per quantity ofsorbent [kg] in the presence of different concentrations of NaClaccording to Example 4.

FIGS. 5 and 6: FIGS. 5 and 6 show the variation over time from Example 5for the absorption of copper of a sorbent from Example 1.

FIG. 7: FIG. 7 shows the binding capacity for copper after regenerationof the sorbent after various cycles according to Example 6.

FIG. 8: FIG. 8 shows the comparison of the copper binding by multiplycoated sorbents with a singly coated sorbent according to Example 7.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In one embodiment of the present invention, a sorbent comprises a poroussupport material coated with an amino group-containing polymer, whereinthe concentration of the amino groups of the sorbent determined bytitration is at least 600 μmol/mL, based on the total volume of thesorbent.

In a further embodiment of the present invention it is preferred thatthe concentration of the amino groups of the sorbent determined bytitration is at least 800 μmol/mL, more preferably at least 1000μmol/mL, still more preferably at least 1200 μmol/mL and most preferablyat least 1500 μmol/mL sorbent. The upper limit of the concentration ofthe amino groups of the sorbent according to the invention determined bytitration is limited by the spatial feasibility or the maximum possibledensity of the arrangement of the amino groups in the aminogroup-containing polymer and is at most about 4000 μmol/mL, morepreferably 3000 μmol/mL and most preferably about 2500 μmol/mL. Theconcentration of the amino groups of the sorbent determined by titrationis understood to mean the concentration which is obtained according tothe analytical method stated in the examples section of this applicationby breakthrough measurement with 4-toluenesulphonic acid.

Furthermore, it is preferred that the sorbent according to the inventionhas a ratio of the mass of the amino group-containing polymer to thetotal volume of the pores of the porous support material of greater thanor equal to 0.1 g/mL, more preferably greater than or equal to 0.125g/mL, still more preferably of greater than or equal to 0.15 g/mL andmost preferably greater than or equal to 0.20 g/mL. Here too, physicallimits are set to the upper limit of the said ratio, however preferablyabout at most 0.5 g/mL, more preferably at most 0.4 g/mL and mostpreferably at most 0.3 g/mL.

The mass of the amino group-containing polymer can be determined by theincrease in the tamped density compared to the support materialaccording to DIN 53194. The total volume of the pores [V] of the poroussupport material can be determined by the solvent absorption capacity(WAC) of the porous support material. The pore volume [vol. %] can alsobe determined likewise. Here, in each case, this is the volume of thefreely accessible pores of the support material, since only this can bedetermined via the solvent absorption capacity. The solvent absorptioncapacity states what volume of a solvent is necessary to fill the porespace of one gram of dry sorbent (preferably stationary phase)completely. As the solvent here, both pure water or aqueous media andalso organic solvents such as dimethylformamide can be used. If thesorbent increases its volume (swelling) on wetting, the quantity ofsolvent used for this is automatically detected. For the measurement ofthe WAC, an exactly weighed quantity of dry sorbent is thoroughly wettedwith an excess of effectively wetting solvent and excess solvent isremoved from the inter-particle volume by centrifugation. During this,solvent within the pores of the sorbent is retained. The mass of theretained solvent is determined by weighing and converted into the volumevia the density. The WAC of a sorbent is reported as volume per gram drysorbent (mL/g).

The coating of the amino group-containing polymer on the porous supportmaterial is preferably present in the form of a hydrogel. This is inparticular because the amino group-containing polymer has the aforesaidhigh concentration of amino groups. A hydrogel is here understood tomean a solvent- (preferably water-) containing, but solvent-solublepolymer, the molecules of which are chemically, e.g. by covalent orionic bonds, or physically, e.g. by entanglement of the polymer chains,linked into a three-dimensional network. Because of built-in polar(preferably hydrophilic) polymer components, they swell in the solvent(preferably water) with considerable volume increase, without howeverlosing their material cohesion. It is known of hydrogels from the stateof the art that they to some extent lose their properties irreversiblywhen they are dried. In the present application, however, the hydrogelsdo not lose their properties, since they are chemically and mechanicallystabilized by the porous support material. The amino group-containingcoating is then present in particular as a hydrogel in the sorbentaccording to the invention, if this is present swollen in a solvent,i.e. in particular during the use for the binding of metals fromsolutions described below.

The porous support material is preferably a mesoporous or macroporoussupport material. The average pore size of the porous support materialpreferably lies in the range from 6 nm to 400 nm, more preferably in therange from 10 to 300 nm and most preferably in the range from 20 to 150nm. A pore size in the stated range is important in order to ensure thatthe binding capacity is sufficiently high. For the case of too small apore size, the amino group-containing polymer on the surface of theporous support material can block the pores and the internal volume ofthe pores is not filled with amino group-containing polymer.Furthermore, it is preferred that the porous support material has a porevolume in the range from 30 to 90 vol. %, more preferably from 40 to 80vol. % and most preferably from 60 to 70 vol. %, in each case based onthe total volume of the porous support material.

The average pore size of the porous support material can be determinedby the pore filling method with mercury according to DIN 66133.

The porous support material can comprise an organic polymer, aninorganic material or a composite material of organic polymers andinorganic materials or consist thereof.

In order to be able to provide a sorbent which has a high sorbentstability over a range from pH 0 to pH 14, it is preferred if the poroussupport material is an organic polymer.

Preferably, the organic polymer for the porous support material isselected from the group which consists of polyalkyl, preferably with anaromatic unit in the side-chain (that is, bound to the polyalkyl chain),polyacrylate, polymethacrylate, polyacrylamide, polyvinyl alcohol,polysaccharides (e.g. starch, cellulose, cellulose esters, amylose,agarose, sepharose, mannan, xanthan and dextran), as well as mixturesthereof. Most preferably, the organic polymer is polystyrene or aderivative of polystyrene, which is preferably a copolymer ofpolystyrene (or derivative of polystyrene) and divinylbenzene. If theorganic polymer bears an aromatic unit, then this is preferably presentsulphonated. In a quite particularly preferred embodiment of the presentinvention, the organic polymer is a sulphonated crosslinkedpoly(styrene-co-divinylbenzene) or a derivative thereof.

If the porous support material is an inorganic material, or it comprisesan inorganic material, the inorganic material is preferably an inorganicmineral oxide selected from the group which consists of silicon oxide,aluminium oxide, magnesium oxide, titanium oxide, zirconium oxide,fluorosil, magnetite, zeolites, silicates (e.g. kieselguhr), mica,hydroxyapatite, fluoroapatite, metal-organic base structures, ceramics,glass, porous glass (e.g. Trisoperl), metals, e.g. aluminium, silicon,iron, titanium, copper, silver and gold, graphite and amorphous carbon.Particularly preferably, the inorganic porous support material is asilicon dioxide or aluminium oxide, in particular silicon dioxide. Thesilicon dioxide is preferably silica gel.

In particular for reasons of the use in a wide pH range, in particularin the basic range, the porous support material is preferably an organicpolymer.

The porous support material used according to the invention can be ofhomogeneous or heterogeneous composition, and therefore in particularincorporates materials which are made up of one or more of the aforesaidmaterials, for example in multilayer compositions.

The porous support material is preferably a particulate material with anaverage particle size in the range from 5 to 2000 μm, more preferably inthe range from 10 to 1000 μm. The porous support material can also be alamellar or fibrous material, such as for example a membrane or a foam.The external surface of the porous support material can thus be flat(lamellae, films, discs, membranes, fibre fabric or non-fibrous fabric)or curved (either concave or convex: spherical, granules, (hollow)fibres, tubes or capillaries).

As mentioned above, the porous support material is coated with an aminogroup-containing polymer which consists of individual polymer chains orcomprises these. The polymer chains are preferably covalently linkedtogether. The amino group-containing polymer is preferably notcovalently linked with the surface of the porous support material.

The use of a non-covalently surface-bound crosslinked polymer as aminogroup-containing polymer on the porous support material also has thefollowing three advantages: (1) flexibility of the polymer, since it isnot covalently bound to the surface of the porous support material; (2)the crosslinking of the amino group-containing polymer ensures that thefilm remains on the surface of the porous support material and is notlost during the use of the sorbent; (3) the thickness of the aminogroup-containing polymer can be selected to be of appropriate size onthe support material when the polymer is not covalently bound to thesupport material.

Adequate flexibility and permeability of the amino group-containingpolymer is important so that several of the amino groups can come into aconformation which enables the metals to be multiply boundco-ordinately.

The high metal binding capacity of the sorbents according to theinvention or of the sorbents produced according to the followingprocesses according to the invention was surprising for the inventorsfor the following reasons:

-   -   in spite of the almost complete filling of the pores of the        support material with the amino group-containing polymer, the        pores are accessible for the metals owing to the permeability of        the polymer, as a result of which the sorbent according to the        invention has a high metal binding capacity. This was all the        more astonishing since polymer standards from inverse size        exclusion chromatography exhibit no accessibility or        permeability. This was also to be observed to over 90% even for        the smallest standards with 450 Da.    -   In contrast to normal chromatographic sorbents and metal-binding        sorbents, which are based on the principle of surface        functionalization, it was surprisingly found through the high        metal-binding property that the present invention utilizes the        entire volume of the polymer responsible for the binding and not        only the surface thereof, i.e. the amino group-containing        polymer together with the solvent containing the metals forms a        so-called hydrogel, in which the polymer network exhibits        nanoporosity. This has the effect that the metal binding        capacity is not determined only by the surface of the support        material, but rather by the volume of the polymer applied.    -   The high metal binding capacity of the sorbents according to the        invention or sorbents produced according to the invention is due        to the formation of chemical complexes between groups of the        amino group-containing polymer and the metals to be bound. These        groups can be the amino groups themselves, or can be residues        which have Lewis base properties, which are bound to the amino        group-containing polymer (as described below). This for example        results in the advantage of the high salt tolerance and binding        capacity in the acidic medium compared to classical ion        exchangers.    -   In parallel to the formation of chemical complexes via which the        metals are bound, the phase still also has a very high binding        capacity for anions, e.g. sulphate, phosphate, nitrite, nitrate,        chromate, arsenate, etc.

The amino group-containing polymer on the sorbent according to theinvention is preferably a polymer which has primary and/or secondaryamino groups. It can be a polymer of the same repeating units(polymerized monomers), but it can also be a copolymer which preferablyhas simple alkene monomers or polar, inert monomers such asvinylpyrrolidone as comonomers.

Examples of the amino group-containing polymer are the following:polyamines, such as any polyalkylamines, e.g. polyvinylamine andpolyallylamine, polyethyleneimine, polylysine etc. Among these,polyalkylamines are preferred, and polyvinylamine and polyallylaminestill more preferred, with polyvinylamine being particularly preferred.

According to a preferred embodiment of the sorbent according to theinvention, the amino group-containing polymer has a degree ofcrosslinking of at least 2%, based on the total number of crosslinkablegroups in the amino group-containing polymer. More preferably, thedegree of crosslinking lies in the range from 2.5 to 60%, morepreferably in the range from 5 to 50% and most preferably in the rangefrom 10 to 40%, in each case based on the total number of crosslinkablegroups in the amino group-containing polymer. The degree of crosslinkingcan be adjusted with the appropriately desired quantity of crosslinkingagent. Here it is assumed that 100 mol. % of the crosslinking agentreacts and forms crosslinkages. This can be verified by analyticalmethods such as by MAS-NMR spectroscopy and quantitative determinationof the quantity of the crosslinking agent relative to the quantity ofthe polymer used. This method is to be preferred according to theinvention. The degree of crosslinking can, however, also be determinedby IR spectroscopy based on, for example, C—O—C or OH-vibrations using acalibration curve. Both methods are standard analytical methods for aperson skilled in the art in this field. If the degree of crosslinkinglies above the stated upper limit, the polymer coating of the aminogroup-containing polymer is not flexible enough and results in a lowermetal binding capacity. If the degree of crosslinking is below thestated lower limit, the polymer coating is not sufficiently stable onthe surface of the porous support material.

The crosslinking agent has two, three or more functional groups throughthe binding of which to the polymer the crosslinking takes place. Thecrosslinking agent which is used for crosslinking the aminogroup-containing polymer is preferably selected from the group whichconsists of dicarboxylic acids, tricarboxylic acids, urea, bis-epoxidesor tris-epoxides, diisocyanates or triisocyanates, and dihaloalkylene ortrihaloalkylene, with dicarboxylic acids and bis-epoxides beingpreferred, such as for example terephthalic acid, biphenyldicarboxylicacid, ethylene glycol diglycidyl ether and1,12-bis-(5-norbornene-2,3-dicarboximido)-decanedicarboxylic acid, withethylene glycol diglycidyl ether and1,12-bis-(5-norbornene-2,3-dicarboximido)-decanedicarboxylic acid beingmore preferred. In one embodiment of the present invention, thecrosslinking agent is preferably a linear, conformationally flexiblemolecule with a length between 4 and 20 atoms.

The preferred molecular weight of the amino group-containing polymer ofthe sorbent according to the invention preferably lies in the range from5000 to 50,000 g/mol, which applies in particular for the polyvinylamineused.

The sorbent according to the invention can, in a further embodiment,also have organic residues which are bound onto the aminogroup-containing polymer and have the nature of a Lewis base. Here it isparticularly preferred that the organic residue is bound onto an aminogroup of the amino group-containing polymer. Also it is particularlypreferred that the amino group onto which the organic residue is boundafter the binding is a secondary amino group, so that this also stilldisplays sufficient Lewis basicity, but without being stericallyhindered.

In a further embodiment, the present invention also relates to a processfor the production of a sorbent, preferably a sorbent according to theinvention, which contains the following steps (preferably in the statedorder):

-   -   (a) provision of a porous support material;

(b) application of an amino group-containing polymer onto the poroussupport material by a pore filling method;

(c) removal of the solvent used in the pore filling method; (d)repetition of steps (b) and (c); and

-   -   (e) crosslinking of the amino group-containing polymer.

In the process according to the invention for the production of asorbent, the porous support material provided in step (a) is one asmentioned above in connection with the sorbent according to theinvention. The preferred embodiments mentioned there apply here to thesame extent.

In step (b) of the process according to the invention, a non-crosslinkedamino group-containing polymer, as is described above in connection withthe amino group-containing polymer of the sorbent according to theinvention, is preferably used. The preferred embodiments mentioned thereapply here to the same extent.

The pore filling method in step (b) of the application of the aminogroup-containing polymer onto the porous support material in the processaccording to the invention entails the advantage compared toconventional impregnation processes that overall a larger quantity ofamino group-containing polymer can be applied onto the porous supportmaterial, as a result of which the binding capacity for metals isincreased. This results in the aforesaid surprising advantages.

The pore filling method is in general understood to mean a specialcoating method in which a solution which contains the aminogroup-containing polymer, is applied onto the porous support material inthe quantity which corresponds to the total volume of the pores of theporous support material. Here, the total volume of the pores of theporous support material in step (b), i.e. the first application, isdetermined beforehand as stated above.

In step (c) of the process according to the invention, the solvent usedfor the pore filling method is preferably removed by drying the materialat temperatures in the range from 40° C. to 90° C., more preferably inthe range from 50° C. to 70° C. and most preferably in the range from50° C. to 60° C. During this, drying is in particular effected at apressure in the range from 0.01 to 1 bar, more preferably at a pressurein the range from 0.1 to 0.5 bar.

It is an essential step of the process according to the invention forthe production of a sorbent that in a step (d) after the drying orremoval of the solvent from the first step of the application by porefilling method, the steps (b) and (c) of the application of an aminogroup-containing polymer onto the porous support material by a porefilling method are repeated. For this, the total volume of the poreswhich is available for the repeated application of the aminogroup-containing polymer onto the porous support material is determinedafter step (b) by differential weighing of the wet and the dry material.In a further embodiment of the process according to the invention, it ismoreover preferred that the steps (b) and (c) are repeated at leasttwice. The total volume of the pores available for the pore fillingmethod is also determined by differential weighing of the wet and thedry materials before the second repetition of steps (b) and (c). Therepetition of steps (b) and (c) preferably takes place in the statedorder.

After the steps of the application of the amino group-containingpolymer, the crosslinking of the amino group-containing polymer takesplace in a step (e), preferably by the crosslinking agent stated inconnection with the sorbent according to the invention. All featuresstated above in connection with the sorbent according to the inventionwith regard to the crosslinking also apply to the production processaccording to the invention.

It is further preferred that between the multiple steps of theapplication of an amino group-containing polymer onto the porous supportmaterial by a pore filling method, no crosslinking of the aminogroup-containing polymer takes place.

Preferably the removal of the solvent used in the pore filling methodeach time is effected by drying in a ploughshare dryer, since this stepcan be markedly accelerated thereby.

In a further embodiment, in the process according to the invention thesteps (b) and (c) are repeated before the step (e) sufficiently oftenthat the concentration of the amino groups of the sorbent determinedafter step (e) by titration is at least 600 μmol/mL, more preferably atleast 800 μmol/mL, still more preferably at least 1000 μmol/mL and mostpreferably at least 1200 μmol/mL, in each case based on the total volumeof the sorbent. The upper limits of the concentration of the aminogroups of the sorbent stated above in connection with the sorbentaccording to the invention are also the upper limits preferred in theprocess according to the invention.

In a further embodiment of the process according to the invention, it ispreferred that the ratio of the mass of the amino group-containingpolymer to the total volume of the pores of the porous support materialafter step (d) is greater than or equal to 0.1 g/mL, more preferablygreater than or equal to 0.125 g/mL, and most preferably greater than orequal to 0.15 g/ml. The upper limit of this ratio is preferably about atmost 0.5 g/mL, more preferably at most 0.4 g/mL and most preferably atmost 0.3 g/mL.

In the pore filling method in step (b) of the process according to theinvention, as solvent for the amino group-containing polymer, one inwhich the amino group-containing polymer is soluble is preferably used.The concentration of the amino group-containing polymer in the solventused for the pore filling method in step (b) of the process according tothe invention preferably lies in the range from 5 g/L to 200 g/L, morepreferably in the range from g/L to 180 g/L, most preferably in therange from 30 to 160 g/L. A concentration below the stated lower limithas the disadvantage that the steps (b) and (c) would have to beperformed too often in order to achieve the desired concentration of theamino groups of the sorbent determined by titration, which ensures asufficient binding capacity for metals. A concentration above the statedupper limit does not ensure that the polymer can penetrate to asufficient extent into the pores of the porous support material.

In a further embodiment of the process according to the invention it ispreferred that in a step (f)—preferably after the step (e)—an organicresidue which has the nature of a Lewis base is bound onto the aminogroup-containing polymer. Here it is particularly preferred that theorganic residue is bound onto the amino groups of the aminogroup-containing polymer. It is further preferred here that after thebinding of the organic residue, the amino groups are present assecondary amino groups, so that their Lewis basicity is not lost and nosteric hindrance to the binding of the amino groups to the metalsarises. An organic residue which has the nature of a Lewis base isunderstood in particular to refer to residues which enter into complexbonding with the metal to be bound.

Organic residues which contain a Lewis base are for example those whichcontain hetero atoms with free electron pairs, such as N, O, P, As or S.

All preferred embodiments mentioned above in connection with the sorbentaccording to the invention apply to the same extent for the sorbentproduced by the process according to the invention, or for thecomponents used in the process according to the invention.

In a further embodiment, the present invention also relates to a sorbentwhich is obtainable by the process according to the invention, inparticular a sorbent which is obtainable by a process according to theinvention, wherein in a step (f) an organic residue which has the natureof a Lewis base is bound onto the amino group-containing polymer. Such asorbent can through the functionalization with an organic residue alsohave a concentration of the amino groups of the sorbent determined bytitration of less than the limit stated above, and is however inparticular characterized in that through the single or multiplerepetition of steps (b) and (c) in the process according to theinvention, the freely accessible pores of the support material areessentially completely filled with the amino group-containing polymer(this is achieved when the WAC is less than 0.5 wt. %), or the ratio ofthe mass of the amino group-containing polymer to the total volume ofthe porous support material after step (d) lies in the range statedabove. Such a sorbent, which has an organic residue which has the natureof a Lewis base, is also intended to include those sorbents which afterthe removal of the organic residue from the amino group-containingpolymer have a concentration of the amino groups of the sorbentdetermined by titration of at least 600 μmol/mL, based on the totalvolume of the sorbent.

A further embodiment of the present invention relates to the use of asorbent for binding metals from solutions, wherein the sorbent is eithera porous support material coated with an amino group-containing polymer,wherein the concentration of the amino groups of the sorbent determinedby titration is at least 300 μmol/mL, more preferably at least 400μmol/mL, and still more preferably 500 μmol/mL, or wherein the sorbentis a sorbent obtainable by the process according to the invention.

In other words the present invention also relates to a process forbinding metals from solutions using a sorbent, wherein the sorbent iseither a porous support material coated with an amino group-containingpolymer, wherein the concentration of the amino groups of the sorbentdetermined by titration is at least 300 μmol/mL, more preferably atleast 400 μmol/mL, and still more preferably 500 μmol/mL, or wherein thesorbent is a sorbent obtainable by a process according to the invention.

The solutions from which metals are to be bound can according to theinvention be concentrated or dilute, aqueous or non-aqueous, acidic,basic or neutral solutions.

The metals of the present application are preferably metals which arepresent in the said solutions in ionic form or also as metal-ligandcoordination compounds in ionic form. The metals are preferablycomplex-forming metals, i.e. metals which can enter into a metal-ligandcoordination bond. More preferably, the metals are transition metals ormetals of the rare earths, still more preferably noble metals or rareearths. Quite particularly preferably, the metals are copper, nickel andchromium.

In a further embodiment of the use according to the invention, thesolutions from which the metals are to be bound are solutions which havea salt content of alkali metal ions of at least 5 g/l.

Furthermore, the solutions from which the metals are to be bound arepreferably aqueous solutions, in particular also an acidic aqueoussolution, with a pH of 5, more preferably 4 and still more preferably 3.

For binding the metals from solutions, the metal-containing solutionsare brought into contact with the sorbent according to the invention.This can for example take place in a normal column. At the same time,sorbents according to the invention which have been developed forbinding different metals can also be present mixed together. This is asa rule effected through the binding of different organic residues ontothe amino group-containing polymer.

Similarly, the contacting of the sorbent according to the invention withthe metal-containing solution can also be performed in batch mode, i.e.without passage of the solution through a vessel with the sorbent, butrather in the form of a suspension of the sorbent in the solution.

The present invention will now be illustrated on the basis of thefollowing figures and examples, which are however only to be regarded asby way of example:

EXAMPLES SECTION Analytical Methods:

Determination of the concentration of the amino groups of a sorbent bybreakthrough measurement with 4-toluenesulphonic acid (titrationanalysis):

The dynamic anion exchange capacity is determined with a column of thestationary phase to be tested. For this, firstly all exchangeable anionsin the column are exchanged against trifluoroacetate. Then the column isrinsed with an aqueous reagent solution of toluene-4-sulphonic aciduntil this solution emerges again in the same concentration at the endof the column (breakthrough). From the concentration of thetoluene-4-sulphonic acid solution, its flow rate and the area of thebreakthrough in the chromatogram, the quantity of toluene-4-sulphonicacid bound by the column is calculated. The quantity oftoluene-4-sulphonic acid thus determined gives the concentration of theamino groups of the sorbent.

The dynamic anion exchange capacity for toluene-4-sulphonic acid inwater is related to the phase volume and reported in mmol per litre(mM/L).

Example 1: Production of a Sorbent According to the Invention

200 g of a sulphonated polystyrene/divinylbenzene support material(average pore size 30 nm) are weighed into a vessel. This material has apore volume determined from the WAC of 1.48 mL/g. In the first coatingthe pore volume should be 95% filled. The polymer solution for thecoating is prepared. 165.3 g of a polyvinylamine solution (solidscontent 12.1 wt. %) are diluted with 108 g water. The pH of the solutionis adjusted to 9.5 with 7 ml conc. hydrochloric acid. The polymersolution is added to the support and mixed for 3 hrs on the overheadshaker. Next, the coated support is dried for 48 hrs at 50° C. in thevacuum drying cabinet at 25 mBar. The material has lost 197.7 g waterthrough the drying. The material is coated for the second time. Forthis, 165.0 g polyvinylamine solution (solids content 12.1 wt. %) areadjusted to a pH of 9.5 with 6.8 mL conc. HCl and diluted with 20 gwater. The polymer solution is added to the support and mixed for 3 hrson the overhead shaker. Next, the coated support is dried for 48 hrs at50° C. in the vacuum drying cabinet at 25 mBar. The material has lost181.2 g water through the drying. The material is coated for the thirdtime. For this, 165.2 g polyvinylamine solution (solids content 12.1%)are adjusted to a pH of 9.5 with 7.1 mL conc. HCl and diluted with 5 gwater. The polymer solution is added to the support and mixed for 3 hrson the overhead shaker. The phase is then dried to constant weight inthe vacuum drying cabinet at 50° C. and 25 mBar.

The material was coated in 3 steps with a total of 0.20 g PVA per mLpore volume.

The dried material was suspended in 1.5 L isopropanol in a double-jacketreactor and crosslinked with 24.26 g ethylene diglycol diglycidyl etherat 55° C. within 6 hrs.

The coated material is washed with the following solvents: 600 mLisopropanol, 3600 mL 0.1 M HCl, 1800 mL water, 1800 mL 1 M NaOH, 1800 mLwater and 1800 mL methanol.

The material is then dried. Yield 275 g dried material.

Analysis: the concentration of the amino groups determined by titrationis 963 μmol/mL.

Comparison Example 1: Production of a Conventional Sorbent

The conventional sorbent is a silica gel modified with 2-aminoethylsulphide ethyl ((Si)—CH₂—CH₂—S—CH₂—CH₂—NH₂) with a particle size of >45μm (Manufacturer Phosphonics, Supplier Sigma-Aldrich, Catalogue number:743453-10G; 0.8-1.3 mmol/g loading).

The modification can be effected by reaction of silica gel with3-mercapto-propyl-trimethoxysilane and subsequent reaction withethylimine.

Example 2: Use of the Sorbents Produced According to Example 1 andComparison Example 1 for Binding Copper from Aqueous Solutions

For plotting isotherms in FIGS. 1 and 2, the following procedure wasused:

10 samples each of approx. 100 mg of the sorbent are precisely weighedout and in each case incubated with different aqueous Cu-II solutions(as CuSO₄) of different concentration for at least 1.5 hrs. The sorbentis filtered off and the Cu-II concentration in solution determinedphotometrically. From the remaining concentration of copper, thequantity of copper bound is calculated and the isotherms generated.

From the comparison of the isotherms in FIGS. 1 and 2, it can be seenthat the sorbent according to the invention has a considerably higherbinding capacity than the conventional sorbent. From the approximatedrectangular isotherms for the sorbent according to the invention it canbe seen that this shows very strong bonding without actual establishmentof equilibrium. This also allows the almost complete removal of heavymetals from very dilute solutions.

Example 3: Use of the Sorbent Produced According to Example 1 forBinding the Three Transition Metals Nickel, Copper and Chromium from aSolution

In each case 10 samples of a defined quantity of the sorbent areprecisely weighed out and in each case incubated with different aqueousmetal solutions of different concentration for at least 1.5 hrs. Thesorbent is filtered off and the metal concentration in solutiondetermined photometrically or with a metal determination methodaccording to Hach-Lange (preferably photometrically). From the remainingconcentration of metal, the quantity of metal bound is calculated andthe isotherms generated.

From FIG. 3 it can be seen that the sorbent according to the inventionbinds the metals nickel (˜70 mg/g sorbent), copper (˜120 mg/g sorbent)and chromium (˜80 mg/g sorbent) to a high degree. The same could also beshown for solutions with the metals palladium, lead and iridium.

Example 4: Use of the Sorbent Produced According to Example 1 forBinding Metals from Solutions with a High Salt Content

5 samples of approx. 100 mg of the sorbent are precisely weighed out andeach incubated for at least 0.5 hrs with a solution of Cu (asCuSO4*5H2O=50 mg/ml water), which contain 0 M NaCl, 0.01 M NaCl, 0.1 MNaCl, 0.5 M NaCl and 1 M NaCl respectively. Next, the sorbent isfiltered off and the copper concentration in the filtrate determinedphotometrically. From the remaining concentration of metal, the quantityof copper bound is calculated and the isotherms generated.

As can be seen from FIG. 4, even at concentrations of up to 1 M commonsalt, the binding capacity of copper is >100 mg Cu/g sorbent. This showsthat a non-ionic binding mechanism is involved, which thus markedlydiffers from ion exchangers “customary in the trade”.

There is no competition for binding sites of copper with sodium, whichis not complexed. The binding capacity for copper is thus maintained.

This property allows the use of the phase in the treatment of drinking,surface, pit, and waste waters, seawater desalination plants,chloralkali electrolysis etc. in which alkali and alkaline earth metalsubiquitously occurring and present in large excess must not interfere.

Example 5: Binding Rate of a Sorbent Produced According to Example 1

Samples each with approx. 100 mg of the phase are precisely weighed outand incubated with a Cu solution (as CuSO4*5H2O=50 mg/ml water) for thestated period. Next, the sorbent is filtered off and the copperconcentration in the filtrate determined photometrically. From theremaining concentration of metal the quantity of copper bound iscalculated.

FIGS. 5 and 6 show the binding of copper from solutions against time.After about 90 minutes, all binding sites of the sorbent are occupied bycopper. No change in the concentration is to be observed even after 48hours.

Example 6: Reusability of the Sorbent Produced According to Example 1

1 g of the sorbent from Example 1 is weighed out and treated as follows:

-   -   1. Rinsing with 1 M NaOH (3×5 ml)    -   2. water (3×5 ml rinsed).    -   3. Addition of 50 ml Cu (as CuSO₄*5H₂O, 50 mg/ml)    -   4. Incubation for 90 mins    -   5. Filtration    -   6. Determination of the copper concentration in the filtrate        (photometrically) and calculation of the quantity of copper        bound    -   7. Repetition of the procedure

As can be seen from FIG. 7, the binding capacity of copper remainsunimpaired after 10 cycles of regeneration and reuse of the sorbentafter 10 cycles (with the exception of cycles 5 and 6) even withtreatment with 5 M HCL and 1 M NaOH.

Example 7: Comparison of Multiply Coated Sorbents with a Singly CoatedSorbent Production of a Singly Coated Sorbent on a Silica Support:

100 g silica gel AGC D-50-120A (average pore size 12 nm) are weighedinto a vessel. This material has a pore volume determined from the WACof 1.12 mL/g. The polymer solution for the coating is prepared. 79.6 gof a polyvinylamine solution (solids content 11.3 wt. %) are dilutedwith 20 g water. The pH of the solution is adjusted to 9.5 with 3 mlconc. hydrochloric acid. The polymer solution is added to the supportand mixed for 6 hrs on a screening machine. Next, the coated support isdried for 48 hrs at 50° C. in the vacuum drying cabinet at 25 mbar.

The material was coated with 0.08 g PVA per mL pore volume.

The dried material was suspended in 0.5 L isopropanol in a double-jacketreactor and crosslinked with 3.64 g ethylene diglycol diglycidyl etherat 55° C. within 6 hrs.

The coated material is washed with the following solvents: 400 mLisopropanol, 1200 mL 0.1 M HCl, 400 mL water, 800 mL 0.5 M triethylaminein water, 600 mL water and 600 mL methanol.

The material is then dried. Yield 108.0 g dried material.

Analysis: the concentration of the amino groups determined by titrationis 593 μmol/mL.

Production of a Doubly Coated Sorbent on a Silica Support:

250 g silica gel AGC D-50-120A (average pore size 12 nm) are weighedinto a vessel. This material has a pore volume determined from the WACof 1.12 mL/g. The polymer solution for the coating is prepared. 200 g ofa polyvinylamine solution (solids content 11.3 wt. %) are diluted with60 g water. The pH of the solution is adjusted to 9.5 with 7.5 ml conc.hydrochloric acid. The polymer solution is added to the support andmixed by vibration for 6 hrs on the screening machine. Next, the coatedsupport is dried for 48 hrs at 50° C. in the vacuum drying cabinet at 25mbar. The material has lost 230 g water through the drying. The materialis coated for the second time. For this, 200 g polyvinylamine solution(solids content 11.3 wt. %) are adjusted to a pH of 9.5 with 6.8 mLconc. HCl and diluted with 23 g water. The polymer solution is added tothe support and again mixed by vibration for 6 hrs on the screeningmachine. Next, the coated support is dried for 48 hrs at 50° C. in thevacuum drying cabinet at 25 mbar.

The material was coated with 0.16 g PVA per mL pore volume.

The dried material was suspended in 1.5 L isopropanol in a double-jacketreactor and crosslinked with 18.2 g ethylene diglycol diglycidyl etherat 55° C. within 6 hrs.

The coated material is washed with the following solvents: 1000 mLisopropanol, 3000 mL 0.1 M HCl, 1000 mL water, 2000 mL 0.5 Mtriethylamine in water, 1500 mL water and 1500 mL methanol.

The material is then dried. Yield 308 g dried material.

Analysis: the concentration of the amino groups determined by titrationis 1254 μmol/mL.

Production of a Triply Coated Sorbent on a Silica Support:

250 g silica gel AGC D-50-120A (average pore size 12 nm) are weighedinto a vessel. This material has a pore volume determined from the WACof 1.12 mL/g. The polymer solution for the coating is prepared. 199 g ofa polyvinylamine solution (solids content 11.3 wt. %) are diluted with60 g water. The pH of the solution is adjusted to 9.5 with 7.6 ml conc.hydrochloric acid. The polymer solution is added to the support andmixed by vibration for 6 hrs on the screening machine. Next, the coatedsupport is dried for 48 hrs at 50° C. in the vacuum drying cabinet at 25mbar. The material has lost 231 g water through the drying. The materialis coated for the second time. For this, 200 g polyvinylamine solution(solids content 11.3 wt. %) are adjusted to a pH of 9.5 with 7.0 mLconc. HCl and diluted with 24 g water. The polymer solution is added tothe support and again mixed by vibration for 6 hrs on the screeningmachine. Next, the coated support is dried for 48 hrs at 50° C. in thevacuum drying cabinet at 25 mbar. The material has lost 210 g waterthrough the drying. The material is coated for the third time. For this,199 g polyvinylamine solution (solids content 11.3 wt. %) are adjustedto a pH of 9.5 with 7.0 mL conc. HCl and diluted with 4 g water. Thepolymer solution is added to the support and again mixed by vibrationfor 6 hrs on the screening machine. Next, the coated support is driedfor 48 hrs at 50° C. in the vacuum drying cabinet at 25 mbar.

The material was coated with 0.24 g PVA per mL pore volume.

The dried material was suspended in 1.5 L isopropanol in a double-jacketreactor and crosslinked with 27.3 g ethylene diglycol diglycidyl etherat 55° C. within 6 hrs.

The coated material is washed with the following solvents: 1000 mLisopropanol, 3000 mL 0.1 M HCl, 1000 mL water, 2000 mL 0.5 Mtriethylamine in water, 1500 mL water and 1500 mL methanol.

The material is then dried. Yield 330 g dried material.

Analysis: the concentration of the amino groups determined by titrationis 1818 μmol/mL.

FIG. 8 shows unambiguously that the binding capacity with the doubly andthe triply coated sorbent increases drastically compared to the singlycoated sorbent.

Comparison Example 2: Production of a Sorbent According to Example 2 ofDE 10 2011 107 197 A1

As the base for the sorbent, Amberchrom CG1000S from Rohm & Haas isused. This is sulphonated as follows: for this, 165 mL conc. H₂SO₄ areplaced in a temperature-controllable 250 mL reactor. 30.0 g of thesupport material are added to the sulphuric acid and the weighing bottlethen rinsed three times in each case with 20 mL conc. sulphuric acid.After the addition of the support material, the suspension is stirredand maintained at 80° C. After 3 hrs reaction time, the suspension isdischarged from the reactor and distributed into two 150 mL syringes.The sulphuric acid is removed under suction and the phase successivelyrinsed with 200 mL diluted (62%) sulphuric acid, 125 mL water, 175 mLmethanol, 125 mL water and finally with 175 mL methanol. The phase issuction dried and then dried at 50° C. under vacuum. The waterabsorption capacity or the pore volume of the resulting sulphonatedpolystyrene is determined by weighing the dried, sulphonatedpolystyrene, treating with the same volume of water and thencentrifuging off excess water. The water present in the pores remains inplace during this.

For the coating of the polystyrene, an aqueous polyvinylamine solutionis prepared, which consists of polyvinylamine with an average molarweight of 35,000 g/mol. The pH is adjusted to 9.5. The quantity ofpolyvinylamine here is 15% of the polystyrene to be coated, and thevolume of the solution is 95% of the determined pore volume of thepolystyrene. The polyvinylamine solution together with the polystyreneis placed in a firmly closed PE bottle and shaken at high frequency for6 hours on a screening shaker. During this, attention must be paid toadequate mixing. After the procedure, the polyvinylamine solution hasworked itself into the pores of the polystyrene. The polystyrene is thendried to constant weight at 50° C. in the vacuum drying cabinet.

For the crosslinking of the polyvinylamine, the coated polystyrene istaken up in three times the volume of isopropanol and treated with 5%diethylene glycol diglycidyl ether, based on the amino group count ofthe polyvinylamine. The reaction mixture is stirred for six hours in thereactor at 55° C. Next, it is transferred onto a glass suction filterand rinsed with 2 bed volumes isopropanol, 3 bed volumes 0.5 M TFAsolution, 2 bed volumes water, 4 bed volumes 1 M sodium hydroxidesolution and finally 8 bed volumes water.

Analysis: the concentration of the amino groups determined by titrationis 265 μmol/mL.

1. Sorbent, comprising a porous support material coated with an aminogroup-containing polymer, wherein the concentration of the amino groupsof the sorbent determined by titration is at least 600 μmol/mL, based onthe total volume of the sorbent.
 2. Sorbent according to claim 1,wherein the ratio of the mass of the amino group-containing polymer tothe total volume of the pores of the porous support material is greaterthan or equal to 0.1 g/mL.
 3. Sorbent according to claim 1, wherein thepore volume of the porous support material lies in the range from 30 to90 vol. %, based on the total volume of the porous support material. 4.Sorbent according to claim 1, wherein the porous support material has anaverage pore size in the range from 6 nm to 400 nm.
 5. Sorbent accordingto claim 1, wherein the porous support material comprises an organicpolymer, an inorganic material or a composite material of organicpolymer and inorganic material.
 6. Sorbent according to claim 1, whereinthe amino group-containing polymer is a polyalkylamine.
 7. Sorbentaccording to claim 1, wherein the amino group-containing polymer is acrosslinked polymer and/or is present not covalently linked with theporous support material.
 8. Process for the production of a sorbent,which comprises the following steps: (a) providing a porous supportmaterial; (b) applying an amino group-containing polymer onto the poroussupport material by a pore filling method; (c) removing solvent used inthe pore filling method; (d) repeating steps (b) and (c); and (e)crosslinking of the amino group-containing polymer.
 9. Process accordingto claim 8, wherein the steps (b) and (c) are repeated before the step(e) sufficiently often that the concentration of the amino groups of thesorbent determined after step (e) by titration is at least 600 μmol/mL,based on the total volume of the sorbent.
 10. Process according to claim8, wherein the ratio of the mass of the amino group-containing polymerto the total volume of the pores of the porous support material afterstep (d) is greater than or equal to 0.1 g/mL.
 11. Process according toclaim 8, wherein step (c) is performed at a temperature in the rangefrom 40 to 80° C. and/or a pressure in the range from 0.01 bar to 1 bar.12. Process according to claim 8, wherein the concentration of the aminogroup-containing polymer in the solvent used for the pore filling methodin step (b) lies in the range from 5 g/L to 200 g/L.
 13. Processaccording to claim 8, wherein in a step (f) an organic residue which hasthe nature of a Lewis base is bound onto the amino group-containingpolymer.
 14. Sorbent which is obtainable according to a process of claim8.
 15. A process for binding metals from solutions, comprisingcontacting a solution containing metal with a sorbent, wherein thesorbent is a porous support material coated with an aminogroup-containing polymer, wherein the concentration of the amino groupsof the sorbent determined by titration is at least 300 μmol/mL.